<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            /* 盒子尺寸=width/height+边框线粗细 */
            width: 380px;
            height: 380px;
            background-color: green;
            border:10px solid black;
            /* border-方位：粗细像素 线形 颜色 */
            /* 具体border-width/style/color */
            /* solid 实线    dashed虚线    dotted点线 */
        
        }
    </style>
</head>
<body>
    <div>这是一个盒子</div>
</body>
</html>